Temperature is one of the major factors that regulate cell morphology and physiology as well as the byproducts of the microalgal biomass. A high temperature generally accelerates the metabolism of microalgae and a low temperature can inhibit growth (Munoz and Guieysse, 2006).

The optimum temperature for growth varies among species of microalgae (Ono and Cuello, 2003). High temperatures during the day have a favorable effect on growth rates due to photosynthesis. High temperatures at night are not desired in microalgal cultivation due to the increased respiration rate; they result in a high expenditure of cellular energy and consequent reduction of cellular concentration.

The temperature also influences other factors that are important for cultivation, such as the ionic balance of water, pH, and solubility of O2 and CO2. Different species of microalgae are affected by temperature at different levels (Park et al., 2011). In the case of combustion gases emitted in power plants, the gas temperatures reach 120 °C. In this case, the rate of CO2 biofixation may depend on the installation of a heat exchange system or the use of thermo­philic species. The solubility of O2 and CO2 increases the temperature and results in the fix­ation of high concentrations of O2 by oxigenase of RuBisCO. Thus the affinity for RuBisCo by CO2 decreases with increasing temperature (Kumar et al., 2011).

The temperature of cultivation in the photobioreactor is determined by the air temperature, the duration of solar radiation, and the relative humidity of air. The depth and the surface of the culture and the material of construction of the photobioractor are factors that stabilize the temperature of the culture. Mechanisms of temperature control cause significant changes in the design of a photobioreactor. With no temperature control, a closed photobioreactor can reach values of 10-30 °C above ambient temperature. Some mechanisms of temperature control in closed photobioreactors include immersion of the culture in water, spraying with water, shading, or incorporating a heat exchanger with the photobioreactor (Wang et al.,

2012) . In raceway-type photobioreactors, the temperature is generally greenhouse controlled. At low temperatures the greenhouse is kept closed, maintaining the temperature. On hot days the sides of the greenhouse can be erected, thus reducing the temperature in the inner area where the raceways are located.